Generally water and chilled waters are used in poultry and food processing plants for washing, waste fluming, chilling and clean-up. Traditionally, water has been used on a once through basis. However, due to rising utility costs, scarcity of available fresh water, costly more stringent waste water disposal surcharge and pollution regulations, processors must look at recycling process waters, and, especially chiller overflow waters, to achieve reduced operational costs.
Signficant savings can be attained by recycling some or all of various waste water streams and reducing the amount of fresh water usage. Additional savings are also derived through reduction in sewage volume, waste disposal surcharges and total refrigeration load.
Throughout the world there are many guidelines and regulations controlling reuse of waste chill water. Typically, in the United States of America, the USDA has many strict guidelines for water use at many steps especially in poultry processing but does allow some water recycling. The regulation for reuse of chiller water overflow is outlined in the Code of Federal Regulations (USDA, 1984). This regulation specifies that reconditioned chiller water must have at least a 60% reduction in total micro-organisms micro-organisms including coliform bacteria, Escherichia coil, and salmonella and a light transmission at 500 nm of no less than 60% of that of fresh water in order to permit reuse in place of fresh incoming waters.
Laboratory tests have shown that the contaminant in overflow chill water from poultry chill tanks is composed of fats, oils and grease and micro-organisms that work loose from the surfaces of the carcasses as they pass through the cooling tanks. Typically total suspended solids will be in the 600-800 ppm range and, of which approximately 30% (200-250 ppm) will be large floating particles of grease and fat. The major portion of the suspended solids (55% from 20-5 micron) form the opaque haze and are believed to be emulsified oils of entrapped proteins and lipids together with the bulk of the micro-organisms. The remaining 5-10% of the particulates are less than 5 micron and seem to be even more tightly bound and emulsified globules.
These are many ways to recondition such chiller overflow water. The primary requirements are that the treatments be economical, effective, reliable, easily monitored, and avoid use of chemical additives. Very few, if any, have been able to meet all of these requirements successfully.
As one example, dissolved air flotation (DAF) systems combined with disposable filter cartridges were tried to remove the fats, oil and grease (FOG) combined with the micro-organisms. However, the short life of the disposable type filters (even with attempted air blow-back) and the resultant labor intensiveness preempted success.
Ozonation for producing virtually sterile water was also tested in conjunction with DAF systems but the excessive organic loading required ozone usage well above economical limits.
Precoat filter systems using such materials as diatomaceous earth (DE), celite, etc. also proved too labor intensive, too costly, not very reliable, and, not readily adaptable for automatic operation.
Chemical additives and flocculants to improve filtration proved very costly and also require complete removal from the final reconditioned water prior to reuse so as not to be considered as a "Food Additive". This drawback of complete removal also applies to residual ozone and filter aids.
Basically, the most difficult problem in reconditioning overflow chiller water, is removing the emulsified oils that have encapsulated the proteins and lipids together with the bulk of the microorganisms. These emulsified globules are in the 0.1 micron to 1.0 micron range and can best be separated out with a barrier membrane in the porosity range of at least down to 0.2 micron but such membranes in this micro range must be kept clean for optimal filtration rates and cannot tolerate gross F.O.G. loadings. Therefore, it is necessary to remove the large (1/32" and larger) lumps of fat and grease prior to the microfiltration step.
This invention addresses a process that provides progressive treatment for the removal of the deleterious components in three basic steps and avoids the deficiencies cited in paragraphs above.